Switching arrangement for electrical circuits



H. G. DEWITZ June 17, 1941.

- swmcnme AR Patented June 17, 1941 SWITCHING ARRANGEMENT FOR ELECTRI- CAL CIRCUITS Hilma'r G. Dewitz, Berlln-Neukolln, Germany, as-

signor to Telefunken Gesellscliaft fiir Drahtlose Telegraphic m. b. 11., Berlin, Germany, a corporaiion of Germany Application December 1 3, 1938, Serial No. 245,477

' In Germany December 13, 1937 2 Claims.

The present invention'relates to switching devices especially adapted for low voltage radio frequency work.

For the purpose of switching low potentials especially radio frequency potentials, mechanical switches of various types have been suggested. While it is possible to use oscillating or vibrating switches as well as rotary switches for such work, .it has been found that rocking or vibrating switches such as relays involve not only the drawback that they are extremely dlmcult to adjust but also the drawback that they are subject to rapid wear. It has also been found that in such switches the wear is uneven and that disturbing energy arising in the operation of these switches is extremely serious.

The rotating switches of the kind disclosed in the prior art usually consist of a metallic commutator and carbon or graphite collector brushes.

In some cases steel commutators with bronze collector brushes have been used. However, it has been found that with any of the type of switches mentioned above, it is difllcult to fulfill the exacting requirements of high frequency low potential work.

not generate spontaneously any potentials whatever.

It is particularly this last mentioned condition which is not sufficiently fulfilled in prior known switching arrangementsand this is probably due mostly to the fact that electrical potentials arise between dissimilar metals so that upon making contact small currents known as switch cracking" are produced. I v

It is an object of the present invention to provide a switching arrangement which substantially satisfies all of the above-mentioned requirements.

In describing the present invention, it will be assumed for the sake of definiteness that the problem is to provide a change-over or reversing switch for the connections of an auxiliary an- Some of these requirements may be summarized as follows:

1. Mechanical switches must be arranged so that when the collector brushes pass from one contact or segment to the next, the contacts should not be short circuited in reference to each other.

2. The contact resistance between the commutator and the brushes must be constant and very low. In this connection it has been found that the contact resistance is a function of the material used as well as the brush surface, the brush pressure, and the circumferential speed of the commutator. A copper commutator with copper brushes has been found to combine the smallest brush area and minimum pressure with the lowest contact resistance. However. constructions of this kind have not been used generally for the reason that the contacts wear out rapidly and require constant supervision and replacement. Comparatively favorabl results are obtainable with copper or bronze commutators and carbon collector brushes. However, these metals become coated with an oxide of low conductivity in a very short time with the result that the contact resistance becomes inadmissably high.

3. In view of the smallness of the potentials at the switch, especially when such switches are used in the'communications art, a mechanical switch must be built in such a way that it will tenna or a loop circuit in a homing direction finder. If the vehicle on which the direction finder is mounted is on its proper course and, if the frame or loop whose plane as known is at right angles to the direction of travel of the vehicle is switched, it will be seen that the voltages to be so switched are extremely small, hence in such an instance contact potentials would manifest themselves in a very troublesome way.

The present invention-provides a change-over switching device in the form of a rotary switch having a roller or drmn consisting of one or of several segments of a carbonaceous material or an equivalent arrangement and current collecting brushes which are also composed of a carbonaceous material.

In order to fulfill the condition underlined under 1) above, the present invention provides between the various segments of the rotary switch, intermediate pieces of such a width that a short circuit between two neighboring segments by t I e collector brushes cannot occur. The intermed ate or insertion pieces may consist of an insulator although it is possible to use some other material for this purpose such as, for instance, soft carbonaceous material with interposed suitable insulation pieces.

A change-over switching device as herein disclosed oifers the advantage that the contact reslstance for the same brush cross-sectional area, pressure, and circumferential speed stays constant and low since oxidation of carbon material is impossible. Moreover, because of the use of similar materials, contact potentials are absent.

The invention will be more fully described in the following detailed specification when read in connection with the drawing,

In the drawing, Figures 1A and 1B illustrate a portion of a rotary switch constructed in accord-' invention wherein portions of the insulating frame are composed of conducting material which may be similar to the conducting segments.

- Referring more particularly to Figure 1A and Figure 1B the rotary switch may comprise two segments 0 and d separated by an insertion piece e which is made of -insulation material. It will be noted that in Figure 1A the two top arrows or connectors are separated by the insulating piece e and that the two bottom arrows or connectors are also separated by the insulating piece e, whereas in the Figure 1B the two top arrows or connectors are connected together by the conducting segment c and the two bottom arrows or connectors are connected together by conducting segment d.

In Figure 2, c and d are the contact segments of the rotary switch and are composed preferably of carbon or carbonaceous material. These two segments are disposed on the insulation frame g which is mounted or seated on a shaft 1 which may be driven by a suitable motor, if desired. The current collector brushes are shown at h and k. These may also be made of carbon or carbonaceous material.

In the embodiment shown in Figure 3 it will be noted that inserts n, n are embedded or fitted into the frame. These inserts may be composed of carbon or carbonaceous material. The arrangement shown in Figure 3 oiiers the advantage that wear will be uniform over substantially all of the perlpheryof the change-over switch provided that the pieces n, n are made of material which is substantially the same as regards wear.- ing quality as the segments c, d and furthermore, provided that the insulator g is made of a material which is softer than the carbon material used for the various segments.

While there have been disclosed several embodiments of the invention, it should be understood that various other arrangements could be made without departing from the scope of the invention as covered by the appended claims.

Having described the invention, what is claimed is:.

1. In a rotary type switching device, a rotary shaft, a drum composed of insulating material mounted on said shaft, a plurality of carbon segments inlaid in spaced relation along the cylindric surface of said drum and flush therewith, and carbon brushes in sliding contact with said cylindrlc surface, said carbon segments being positioned on said cylindric surface so as to be in the path of said brushes, the material of which said drum is composed being softer than the carbon segments.

2. In a rotary type switching device, a rotary shaft, a drum composed of insulating material mounted on said shaft, a carbon brush in sliding contact with the cylindric surface of said drum, a plurality of largecarbon segments embedded in the cylindric surface of said drum, flush therewith and in the path of said brush, and a plurality of comparatively small carbon segments embedded in the cylindric surface of said drum, flush therewith and in the path of said brush one between each adjacent pair of said large carbon segments, all of said carbon segments being insulated from. each other on said drum.

HILMAR. G. DEWITZ. 

